Disk drives are capable of storing large amounts of digital data in a relatively small area. Disk drives store information on one or more recording media, which conventionally take the form of circular storage disks (e.g. media) having a plurality of concentric circular recording tracks. A typical disk drive has one or more disks for storing information. This information is written to and read from the disks using read/write heads mounted on actuator arms that are moved from track to track across the surfaces of the disks by an actuator mechanism.
Generally, the disks are mounted on a spindle that is turned by a spindle motor to pass the surfaces of the disks under the read/write heads. The spindle motor generally includes a shaft and a sleeve into which the shaft is inserted. In order to facilitate relative rotation of the shaft and sleeve, one or more bearings are usually disposed between them.
Over the years, storage density has tended to increase, and the size of the storage system has tended to decrease. This trend has lead to greater precision and lower tolerance in the manufacturing and operating of magnetic storage disc drives.
The bearing assembly that supports the storage disk is of critical importance. One bearing design is a fluid dynamic bearing. In a fluid dynamic bearing, a lubricating fluid such as air or liquid provides a bearing surface between a fixed member of the housing and a rotating member of the disk hub. In addition to air, typical lubricants include gas, oil, or other fluids. The relatively rotating members may comprise bearing surfaces such as cones or spheres and hydrodynamic grooves formed on the members themselves. Fluid dynamic bearings spread the bearing surface over a large surface area, as opposed to a ball bearing assembly, which comprises a series of point interfaces. This bearing surface distribution is desirable because the increase bearing surface reduces wobble or run-out between the rotating the fixed members. Further, the use of fluid in the interface area imparts damping effects to the bearing, which helps to reduce non-repeatable run-out. Thus, fluid dynamic bearings are an advantageous bearing system.
In the field of fluid dynamic bearing motors for use in hard disc drives, some prior systems including, but not limited to, small form factor motor designs for mobile applications have been limited by stringent power and ever tightening track density requirements. In the traditional “single-plate” FDB design, axial stiffness is provided by two equally opposing thrust bearings and the bearing lubricant is retained by closing one bearing end and placing a capillary seal at the opposing end. This traditional approach results in two thrust bearing gaps at large diameters, thereby increasing bearing drag and overall motor power.
Furthermore, as motor designs decrease in size, axial space and power constraints become crucial. The limited journal bore length often results in unusual angular stiffness sensitivity. Traditionally, the angular stiffness problem has been addressed by employing large axial thrust bearings to augment the total bearing angular stiffness when axial space does not permit increasing journal span. However, this approach consumes a significant amount of power, and so has become a less favorable solution in smaller disk drives.
Thus, there is a need in the art for an efficient fluid dynamic bearing design that is capable of providing both radial and axial stiffness, especially within a very short axial height envelope.